The present application is generally directed to nanoscale computing and memory circuits and, more particularly, to the characterization of the molecular films employed in such devices. The devices may have more than one stable state (e.g., bi-stable switches) and may be homogeneous or heterogeneous in nature (e.g., may be composed of one or more molecules which are uniformly or nonuniformly distributed throughout). The term “nanoscale” is used to indicate that either the horizontal or vertical dimensions or the electrical pathway between contacts is measured in nanometers.
As feature sizes of integrated-circuit devices continue to decrease, it becomes increasingly difficult to design well-behaved devices. Their fabrication is also becoming increasingly difficult and expensive. Moreover, the number of electrons either accessed or utilized within a device is decreasing, producing increased statistical fluctuations in the electrical properties. In the limit, device operation depends on a single electron, and traditional device concepts must change.
Developments in nanotechnology are directed to solving these problems using new generations of electronic circuitry, having much smaller dimensions than present technology can provide. An advantage of molecular electronic devices is that the device performance characteristics originate from molecular properties. This has several notable implications. First, it means that the devices can potentially scale down in size to nanometer dimensions without significant change(s) in device performance. Second, it also means that the unique electronic properties designed into these molecular structures can be aggregated and designed into solid state devices.
Molecular electronics has the potential to augment or even replace conventional devices with electronic elements, can be altered by externally applied voltages or fields, and has the potential to scale from micron-scale dimension to nanometer-scale dimensions with little change in the device concept. Examples of such molecular electronic devices include, but are not limited to, crossed wires, nanoporous surfaces, and tip addressable circuitry which forms switches, diodes, resistors, transducers and other active components.
For instance, a crossed-wire switch may comprise two wires, or two contacts, for example, with a molecular switching species between the two contacts. Thin single or multiple molecular layers can be formed, for example, by Langmuir-Blodgett (LB) techniques or by a self-assembled monolayer (SAM) on a specific site. The self-assembled switching elements may be integrated on top of a semiconductor integrated circuit so that they can be driven by conventional semiconductor electronics in the underlying substrate. To address the switching elements, interconnections, probes or wires are used. (The term “self-assembled” as used herein refers to a system that naturally adopts some regular pattern because of the identity of the components of the system; the system achieves at least a local minimum in its energy by adopting this configuration.)
Despite its great promise, the area of molecular electronics is still in its infancy. An early step towards molecular computing was to produce a bistable molecular device capable of encoding a logical 1 or 0 such as when switched from a “high” or “on” state to a “low or “off” state. For nanoscale electronic circuits, new materials may be invented with the functions envisioned for them and new processes to fabricate them. Nanoscale molecules with special functions can be potentially used as basic elements for nanoscale computing and memory applications.
For example, a bi-stable molecule, such as rotaxane, pseudo-rotaxane, or catenane, formed between contacts could create a switch at the molecular level. An array of such switches could form logical circuits or memory structures. Application of a voltage across a selected pair of contacts connected by the molecular species of interest would cause the change in state. The term “bi-stable” as applied to a molecule refers herein to a molecule having two relatively low energy states. The molecule may be either irreversibly switched from one state to another (singly configurable) or reversibly switched from one state to another (reconfigurable).
Characterization of both molecular films and the molecules comprising such films generally occurs on a substrate, not in solution, with contacts formed using conventional semiconductor processing techniques. Characterization of such devices has typically been via two contacts normal to the surface of an assembled or transferred film, where the film is akin to a page or set of pages and the contacts are opposing covers of a closed book. This characterization may employ contacts of micron or nanometer scale.
Unfortunately, this method does not allow access to properties at other angles, due to the small thickness of the film and discretely contacting the longitudinal edges of the film (as in the spine of the book) is extremely difficult due to the small thickness of the film. There is a present and future need for a practical technique to perform such non-normal angle characterization and fully investigate sample properties in multiple directions.